送饭上门 is what I have now, but for aesthetic reasons I would like to have a 2 character word. Is
送饭 enough on a restaurant flyer (that's the context I am working with) or do I need the whole four character expression?
送餐 will be the appropriate translation for this case. :)
If you are working for a eatery, "外卖" is more native because you need to get out of the building to bring your customers food.
"送餐" usually appears in hotels or somewhere else like that. It's a bit formal because the food is prepared by advanced chefs and they are finely laid out but they are just sent to your room.
"送饭" is the worst, I suppose.